Operational Base Design

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was last updated at 2:00pm on 29/11/11

The primary
requirements for OBs were that they should be concealed, habitable and reasonably weatherproof. A standard
design was used, comprising an underground chamber with a vertical shaft at one end leading to the main entrance,
and an escape passage at the other end. The entrances were secured with well camouflaged trapdoors.
Because of the camouflage and secrecy associated with these structures, they are generally poorly represented in
records of known sites from the period.

(Above - The training OB at Coleshill we believe served as a prototype. Take a tour of this
OBhere.)

Designs varied from County to County.

Suffolk and Norfolk: The first OBs to be constructed were
built in East Anglia (in Essex and South Suffolk), often by the patrol members themselves and later with the help
of Royal Engineers. Norfolk and Suffolk OBs typically consisted of a main chamber, a so-called 'Elephant' shelter,
which had a curved, corrugated iron roof (similar to a Nissen hut but underground). Main chambers varied in length
from 12-15ft. The end walls could be brick, or earth lined/stabilised with corrugated sheeting. The main chamber
was accessed through a drop-down shaft, either built from brick, or they had earthen walls that were lined with
corrugated sheeting. Most but not all had an underground escape passage of several metres' length that led out the
other end. Both entrance and exit openings were secured with well disguised trapdoors commonly operated with
counterweights.

Lincolnshire: Typical Lincolnshire OBs are sturdily built
structures made from concrete prefabricated panels that were bolted together (rather like a Stanton shelter but
underground), and brick or breezeblock end walls. The main chamber was accessed through a drop-down,
breezeblock-built shaft. Main chambers varied in length from 12-14ft and appear to have been well ventilated. The
walls of emergency exit tunnels were commonly also built from breezeblocks, and a toilet cubicle and even an
ammunition store can often be found incorporated in the structure. Both entrance and exit openings were secured
with well disguised trapdoors or hatches. The use of counterweights appears to have been less common in
Lincolnshire than it was in both Suffolk and Norfolk.

Dorset: Most OBs seem to be built with the standard
Elephant shelter, though 2 chambers seem common. End walls are brick and escape tunnels, where present, were
presumably wood or corrugated iron as most seem to have collapsed. It is known that the Pioneer Corps built at
least one OB. No surviving lids have been found yet, but there is evidence of recessed hatches in a couple of
surviving shafts. Some OBs seem to have been built relatively late on (late 1942).

Scotland: Operational Bases were a ‘variation on a theme’
as compared to some of the Scottish Mainland ones. Improvisation being the operative word and islanders from these
parts were a hardy lot. It was A.G Fiddes-Watt Intelligence Officer (IO) for Number 1 Area; who looked on in sheer
horror as ancient pot sherds were discarded by some members of a patrol while they were hastily constructing their
OB.

Other counties will follow.

These OB plans were sent to us by Jeff Bubble. You can download the full unedited large version here